In general, a polymer electrolyte fuel cell has a structure in which a plurality of single cells exerting a power generation function are stacked on one another. Each of the single cells has a membrane electrode assembly (MEA) that includes a polymer electrolyte membrane (for example, NAFION (registered trademark, made by DuPont Corporation)) and a pair (anode, cathode) of electrode catalyst layers which sandwich the same therebetween. Moreover, this single cell sometimes has a membrane electrode gas diffusion layer assembly that includes a pair (anode, cathode) of gas diffusion layers (GDLs) which sandwich the membrane electrode assembly and serve for dispersing feed gas. Then, the membrane electrode assembly and the membrane electrode gas diffusion layer assembly, which each of the single cells has, are electrically connected to membrane electrode assemblies and membrane electrode gas diffusion layer assemblies of other single cells, which are adjacent thereto, while interposing separators therebetween. The single cells are stacked on and connected to one another as described above, whereby a fuel cell stack is configured. Then, this fuel cell stack is capable of functioning as power generation means usable for various purposes.
A description is briefly made of a power generation mechanism of the polymer electrolyte fuel cell. At an operation time of the polymer electrolyte fuel cell, fuel gas (for example, hydrogen gas) is supplied to an anode side of the single cell, and oxidant gas (for example, atmosphere, oxygen) is supplied to a cathode side thereof. As a result, electrochemical reactions represented by the following Reaction formulae (I) and (II) progress on the anode and the cathode, respectively, and electricity is created.H2→2H++2e−  (I)2H++2e−+(1/2)O2→H2O  (II)
In order to enhance power generation performance, it is important to enhance proton transport properties in Reaction formulae (I) and (II), and it is particularly important to enhance apparent catalytic activity in Reaction formula (II).
Heretofore, in order to achieve the enhancement of the proton transport properties and the apparent catalytic activity a fuel cell of Patent Literature 1 has been proposed. In the fuel cell of Patent Literature 1, a catalyst electrode layer, which has a catalyst, an electron conductor having the catalyst supported thereon, and predetermined proton-conductive resin formed so as to cover the electros conductor, is formed on an electrolyte membrane. Then, this predetermined proton-conductive resin contains at least two or more proton-conductive resins different in molecular weight. Moreover, the molecular weight of the proton-conductive resin present in micropores in aggregates of the electron conductor is smaller than the molecular weight of the proton-conductive resin present in micropores between the aggregates of the electron conductor.